1. Field of the Invention
The present invention relates to a diagnostic device for a catalytic converter which is employed for treating exhaust gas emitted from an internal combustion engine. More particularly, it relates to a catalyst-deterioration diagnostic system which can diagnose the state of a catalyst by the use of the preset operating-state index of an internal combustion engine and can report the diagnosed result through a display, an alarm sound or the like to the driver of a vehicle having the system installed therein.
2. Description of the Related Art
It has been known that, in making the exhaust gas of an internal combustion engine innoxious through oxidizing and deoxidizing reactions, effectively the reactions are promoted by employing a catalyst which contains a plurality of kinds of catalytic components. In this regard, when the catalyst is used for a long term, it deteriorates into a lower conversion efficiency. Therefore, such a step has heretofore been taken that the conversion efficiency of the catalyst is checked mainly at the time of a routine inspection, and that a catalytic converter including the catalyst is replaced when the regulated value of the conversion efficiency is not met. Accordingly, the conversion efficiency is not especially checked till the routine inspection, and a vehicle in which the catalytic converter is installed runs under the unsatisfactory innoxious condition of the exhaust gas in some cases.
Such circumstances unfavorably lead to environmental pollution. Attempts have therefore been made to check the performance or activity of the catalyst at all times by any method, and to actuate a warning device or a countermeasure device when the catalyst is abnormal. Examples will be stated below.
Japanese Patent Application Publication (KOKOKU) No. 2896/1982 discloses a technique wherein oxygen-percentage detectors are respectively mounted before and behind a catalytic converter so as to diagnose the state of the catalytic converter on the basis of the detected values of both the detectors. Concretely, the detectors capable of detecting the oxygen concentrations of exhaust gas are respectively disposed upstream and downstream of the catalytic converter. When the oxygen concentration of the exhaust gas detected by either of the detectors has abnormally fallen outside a preset range until the difference thereof from the output of the other detector has exceeded a preset magnitude, a signal is generated to actuate an alarm device or a device for taking steps to rectify the abnormality.
In addition, according to a technique entitled xe2x80x9cApparatus for Detecting Deterioration of Catalystxe2x80x9d as disclosed in Japanese Patent Application Laid-open No. 249320/1991, the correlation coefficient of the output signals of oxygen sensors mounted before and behind a catalytic converter is calculated so as to diagnose the state of a catalyst with the calculated correlation coefficient.
Further, a method which adopts a sensor for diagnosing the deterioration of a catalyst is disclosed in Japanese Patent Application Laid-open No. 165744/1988. With this method, the catalyst for combustion is so constructed that a catalytic component is carried on a support having a large number of through holes. A basic material in the shape of a rod is inserted into the through hole, and is used as the sensor. The state of the catalyst is diagnosed by measuring the resistance of the rod across both the ends thereof. This method can diagnose the state of the catalyst irrespective of the operating conditions of an engine.
In general, however, the activity of a catalyst varies greatly in dependency on the temperature thereof as illustrated in FIG. 12 of the accompanying drawings, so that the conversion efficiency etc. of the catalyst varies in accordance with the temperature thereof. It is accordingly necessary for the precise diagnosis of the deterioration state of the catalyst to stipulate the temperature of the catalyst on the occasion of the diagnosis or to correct a calculated conversion efficiency in accordance with the temperature of the catalyst at the time of the diagnosis. To this end, however, a temperature sensor for monitoring the temperature of the catalyst is required, resulting in the problem of rise in cost.
The present invention has for its object to provide a catalyst-deterioration diagnostic system which can precisely diagnose the state of a catalyst in correspondence with the temperature thereof, without incurring a rise in cost.
In the first aspect of performance of the present invention, there is provided a temperature estimation apparatus, comprising state detection means for detecting a value of a state variable which correlates with a temperature of a part to have its temperature detected;. memory means for prestoring therein correspondence information which indicate corresponding relations between detected results of the state detection means and temperatures of the part for the temperature detection; and estimation means for estimating the temperature of the part for the temperature detect referring to the correspondence information on the basis of the detected result of the state detection means.
In this case, it is preferable that the part for the temperature detection is a catalyst which cleans exhaust gas of an engine; and that the state variable includes at least one member which is selected from the group consisting of a quantity of intake air, a quantity of fuel injection and r. p. m. (revolutions per minute) of the engine.
In the second aspect of performance of the present invention, there is provided a method of estimating a temperature of a catalyst, comprising the steps of prestoring corresponding relations between temperatures of the catalyst which cleans exhaust gas of an engine and values of a state variable which correlates with the temperatures of the catalyst; and detecting an actual value of the state variable, and then comparing the detected value with the stored corresponding relations, thereby estimating the temperature of the catalyst.
In the third aspect of performance of the present invention, there is provided a catalyst-deterioration diagnostic system for diagnosing a deterioration state of a catalyst, comprising index means for obtaining a value of an index (for example, a conversion efficiency of the catalyst) which is used for deciding the deterioration state of the catalyst; catalyst state estimation means for estimating a state of the catalyst at a time at which the index means has obtained the index value, as to a physical quantity which affects a catalytic action of the catalyst; correction means for correcting the index value obtained by the index means, to a value in a standard state of the catalyst previously set as to the physical quantity, by the use of the estimated result of the catalyst state estimation means; and decision means endowed with a preset criterion value, and for deciding the deterioration state of the catalyst by comparing the index value corrected by the correction means, with the criterion value.
In the fourth aspect of performance of the present invention, there is provided a catalyst-deterioration diagnostic system for diagnosing a deterioration state of a catalyst, comprising index means for obtaining a value of an index (for example, a conversion efficiency of the catalyst) which is used for deciding the deterioration state of the catalyst; decision means endowed with a preset criterion value, and for deciding the deterioration state of the catalyst by comparing the index value obtained by the index means, with the criterion value; catalyst state estimation means for estimating a state of the catalyst at a time at which the index means has obtained the index value, as to a physical quantity which affects a catalytic action of the catalyst; and suspension means endowed with a predetermined range concerning the physical quantity, and for causing the decision means to suspend the decision on condition that a value of the physical quantity obtained by the catalyst state estimation means is outside the predetermined range.
In each of the third and fourth aspects of performance, the catalyst-deterioration diagnostic system may well be so constructed that the catalyst serves to eliminate noxious substances which are contained in exhaust gas of an engine, and that the catalyst state estimation means includes operating-situation detection means for detecting a value of a state variable of the engine as correlates with the physical quantity, memory means for storing therein correspondence information which indicate correlations between values of the state variable and those of the physical quantity, and arithmetic means for determining a value of the physical quantity by referring to the correspondence information on the basis of the detected result of the operating-situation detection means.
In the fifth aspect of performance of the present invention, a catalyst-deterioration diagnostic system for diagnosing a deterioration state of a catalyst, wherein the catalyst serves to eliminate noxious components which are contained in exhaust gas of an engine, comprises: index means for obtaining a value of an index which is used for deciding the deterioration state of the catalyst; operating-situation detection means for detecting a value of that state variable of the engine which correlates with a physical quantity affecting a catalytic action of the catalyst; correction means for correcting the index value obtained by the index means, to a value in a standard state of the catalyst previously set as to the physical quantity, by the use of the detected result of the operating-situation detection means; and decision means endowed with a preset criterion value, and for deciding the deterioration state of the catalyst by comparing the index value corrected by the correction means, with the criterion value.
In the sixth aspect of performance of the present invention, a catalyst-deterioration diagnostic system for diagnosing a deterioration state of a catalyst, wherein the catalyst serves to eliminate noxious components which are contained in exhaust gas of an engine, comprises: index means for obtaining a value of an index which is used for deciding the deterioration state of the catalyst; decision means endowed with a preset criterion value, and for deciding the deterioration state of the catalyst by comparing the index value obtained by the index means, with the criterion value; operating-situation detection means for detecting a value of that state variable of the engine which correlates with a physical quantity affecting a catalytic action of the catalyst; and suspension means endowed with a predetermined range concerning the state variable, and for causing the decision means to suspend the decision on condition that the value of the state variable detected by the operating-situation detection means is outside the predetermined range.
In each of the fourth and sixth aspects of performance, it is preferable that the catalyst-deterioration diagnostic system further comprises alarm means for giving an alarm for the suspension of the decision when the decision has been suspended by the suspension means.
In the seventh aspect of performance of the present invention, a catalyst-deterioration diagnostic system for diagnosing a deterioration state of a catalyst, wherein the catalyst serves to eliminate noxious components which are contained in exhaust gas of an engine, comprises: index means for obtaining a value of an index which reflects the deterioration state of the catalyst; operating-situation detection means for detecting a value of that state variable of the engine which correlates with a physical quantity affecting a catalytic action of the catalyst; correction means for correcting the value detected by the operating-situation detection means, to a value in a standard state of the catalyst previously set as to the index, by the use of the index value obtained by the index means; and decision means endowed with a preset criterion value, and for deciding the deterioration state of the catalyst by comparing the value corrected by the correction means, with the criterion value.
In each of the aspects of performance mentioned above, it is allowed that the physical quantity is a temperature of the catalyst; and that the state variable includes at least one member which is selected from the group consisting of a quantity of intake air, a quantity of fuel injection and r. p. m. (revolutions per minute) of the engine.
According to the present invention thus far summarized, the temperature of the catalyst can be known without using a thermometer. Moreover, since the deterioration state of the catalyst is decided after the correction of the calculated conversion efficiency, it is diagnosed precisely.